Manufacture of gasolinelike hydrocarbons



Feb. 13, 1940. w. w. GARY Er AL MANFACTURE 0F GASOLINELIKE HYDROCARBONS Filed Feb. 15. 1936 kwmkowm ATTORNEY Patented Feb. 13, 1940 UNITED STATES PATENT OFFICE MANUFACTURE F GASOLINELIKE HYDROCARBONS Application February 15, 1936, Serial No. 63,998

1 Claim.

Our invention relates in general to the conversion of normally gaseous hydrocarbons to normally liquid gasolinelike hydrocarbons and more particularly to a process for polymerizing hydrocarbon gases containing both saturated and unsaturated constituents to liquid hydrocarbons having boiling points lying within a gasoline or motor fuel boiling point range.

It is well known that gases resulting from cracking hydrocarbon oil contain various quantitles of hydrogen, methane, ethane, ethylene, propane, propylene, butane, and Ibutylene, and these gases, after separation of hydrogen and methane and controlled amounts of ethane, if desired, to avoid excessive quantities thereof building up in the system, can be readily polymerized either thermally or catalytically. In processes involving thermal polymerization of hydrocarbon gases, it is generally customary to separate the polymerized products into gasoline,

fixed gas containing hydrogen and methane, and

a normally gaseous fraction containing saturated and unsaturated hydrocarbons of from two to four carbon atoms per molecule intermediate the gasoline and xed gas. To accomplish substantially ultimate conversion of the intermediate normally gaseous fraction containing butane, butylene, propane, propylene, ethane, and ethylene, prior processes provide for the recycling thereof to increase the ultimate yield of motor fuel from the normally gaseous hydrocarbons.

Our invention has for an object the provision of an improved operating method and cycles for carrying out a process of the character indicated, including such additional operating results and advantages as may hereafter be found to be contained.

In order to make our invention more clearly understood, we have shown in the accompanying drawing, means for carrying the same into practical effect without limiting the improvement in their useful application to the particular embodiment which, for the purpose of explanation, has been made the subject of illustration.

The single figure is a somewhat diagrammatic elevational view of one form of apparatus capable of carrying out our invention.

Referring to the drawing, there is shown a polymerizing furnace l, having a plurality of interconnected tubes therein for forming a continuous coil, a separator 2, a plurality of fractionators 3, 6 and l, each of which is provided with suitable fractionating plates or trays, and an absorber 5 wherein normally gaseous hydrocarbons are absorbed by a liquid scrubbing medium.

A plurality of accumulators or receivers 8, 9, II and l2 are likewise provided, a separate one being associated with each fractionator.

The accumulator 8 associated with the fractionator 3 functions as a reservoir for the normally gaseous hydrocarbons to be polymerized, the source of these hydrocarbons being hereinafter explained. Normally gaseous hydrocarbons, in liquid condition, and containing saturated and unsaturated constituents of from two to four carbon atoms per molecule, are withdrawn from the accumulator 8 through a line I3 and forced by means of a pump I4 through a heat exchanger I5 and then to the inlet of the polymerizing furnace I. If desired, liquefied hydrocarbon gases in addition to those entering the furnace I through the line I3 may be introduced directly into the furnace .through a line I6. The hydrocarbons passing through the furnace I are heated to a polymerizing temperature of from about 750 to 1250 F. while being maintained under a pressure in excess of 500 lbs. per sq. in. and preferably from 500 to 3000 lbs. per sq. in. to effect polymerization of the gaseous constituents into normally liquid gasolinelike constituents. The hot polymerized products leaving the furnace I are conducted through a line II, controlled by a pressure-control valve I9, to the high-pressure separator 2. Prior to the reduction of pressure on the hot polymerized products, they are appropriately cooled to avoid further reaction thereof. As shown, this cooling may be effected by directly contacting the hot polymerized products with a liquid oil introduced through a line I8, the source of which will be later explained, and by passage through the heat exchanger I5 receiving the normally gaseous hydrocarbons passing to the furnace I.

The separator 2 is preferably maintained at a pressure between about 400 and 600 lbs. per sq. in. and a separation between gaseous and liquid constituents of the polymerized products is effected therein. The gaseous fraction separated in the separator 2 contains hydrogen, methane, ethane, ethylene, propane, propylene, butane, and butylene, and is conducted through a line 2l to the fractionator 3 preferably maintained under a pressure of between about 400 to 600 lbs. per sq. in. The liquid constituents separated in the separator 2 contain the gasolinelike products and heavier oil formed during the polymerization reaction as well as some dissolved normally gaseous hydrocarbons, and is conducted through a line 22, controlled by a pressure-reduction valve 23, to the fractionator 4 preferably maintained under 55 a pressure of between about 250 to 300 lbs. per sq. in. The normally gaseous fraction passing upwardly in the fractionator 3 is therein fractionated to separate therefrom hydrocarbons heavier than butane and butylene.

In one mode of operation, fresh normallygaseous charging stock containing hydrogen, methane, and saturated and unsaturated hydrocarbons of from two to four carbon atoms per molecule, and particularly when it also contains pentane, is introduced into the upper portion of the fractionator 3 by a line 2li. The charge entering the fractionator 3 is therein stripped of lighter constituents and partially fractionated, the lighter constituents containing hydrogen, methane, and saturated and unsaturated hydrocarbons of from two to four carbon atoms per molecule, being conducted through a line 25 and condenser 2E to the accumulator 8. In another mode of operation and particularly when the fresh gases do not contain hydrocarbons heavier than butane and butylene, the fresh charge may be introduced directly into the accumulator d through a pipe 2l.

Hydrocarbons heavier than the C4 fraction are withdrawn from the lower portion of the fractionator 3 through a line 2S, controlled by a pressure-reduction valve 29, and are passed to the fractionator il at an intermediate point thereof above the line 22. The liquid products entering the fractionator i through the lines 22 and 28, due to the lower pressure prevailing therein, are separated into normally gaseous hydrocarbons containing from two to four carbon atoms per molecule which after fractionation pass overhead though a line 3i and condenser 32 to the liquid accumulator 9. The liquefied hydrocarbons in `the accumulator 9 constitute suitable recycle thermally-gaseous stock for reprocessing to obtain the ultimate yield of motor fuel. These liquefied hydrocarbons are passed through a line 33 by a pump 365 to the accumulator 8 wherein they are mixed with the overhead fraction from the fractionator 3 or with this fraction and fresh charge when the fresh charge is introduced directly to the accumulator 8 through the line 2.

Liquid hydrocarbons, containing the desired `gasolinelike constituents, and heavier oil separated within the fractionator d, are conducted through a line 35, controlled by a pressure-reduction valve 36, to the fractionator l. The fractionator 'i is preferably maintained under a pressure of about 10 lbs. per sq. in. or higher, and due to the reduction of pressure on the products entering the fractionator l, the gasolinelike constituents contained in these liquid products are vaporized. The upwardly rising vapors in the fractionator l are therein fractionated to produce an overhead vaporous fraction consisting of gasolinelike constituents of exceptionally high antiknock rating. This overhead fraction is conducted through a line 3l and condenser 38 to the gasoline receiver i2. Polymerized gasoline may be withdrawn from the receiver i2 through a line 39 and passed to suitable storage.

Liquid oil heavier than the desired gasoline collects in the bottom of the fractionator l and may be withdrawn therefrom through a line dii, a part thereof, if desired, being withdrawn from the system through a line lli. This liquid oil may be used, however, in cooling the hot polymerized products leaving the furnace i. In one method of operating our process, a part or all of this heavier oil may be conducted through a line i2 by a pump i3 and introduced through the line it into intimate contact with the hot polymerized products leaving the furnace l and passing through the line il. If desired, oil from an extraneous source may be used as the liquid oil cooling medium or may be mixed with oil passing through the line 2.

Returning now to the high-pressure accumulator 8, the paranic and oleflnic constituents having two to four carbon atoms per molecule are for the most part in liquid condition. Some of these hydrocarbons, however, and substantially all of the hydrogen and methane introduced into the accumulator il do not remain in liquid condition and in accordance with our process are conducted through a line @it to the absorber 5 maintained at a pressure of about 400 lbs. per sq. in. The absorber 5 is provided with suitable plates and trays to assist fractionation therein, as is well understood, and receives a liquid scrubbing medium, such as gas oil, in the upper portion thereof through a line d5. The gaseous hydrocarbons passing upwardly in the absorber are therein contacted with the liquid scrubbing medium by countercurrent contact therewith and the scrubbing medium absorbs constituents of higher molecular weight than methane from the gaseous hydrocarbons. The residual gases, comprising substantially mostly hydrogen and methane and, if desired, controlled amounts of ethane, escape from the top of the absorber 5 through a line d5, while the enriched absorbent passes from the bottom of the absorber 5 through a line di, wherein is located a heat exchanger (it and a pressure-control valve lig, to a fractionating and stripping tower G maintained under a pressure of about from 300 to 400 lbs. per sq. in. Within the fractionator a combined fractionating and stripping action takes place, the enriched absorbent oil introduced through the line il being stripped of the gases absorbed by it in the absorber 5. The bottoms from the fractionator 6 comprise the stripped absorbent oil and are passed through a line 5o and the heat exchanger d8 by a pump 5i to the upper portion of the absorber 5 through the line d5 as absorbent oil therefor. 'I'he absorbent oil may be introduced into the system during the starting up of the process.

Overhead gases from the top of the fractionator ii pass through a line 52, condenser 53, and thence to the accumulator or receiver Ii maintained at substantially the same pressure as the fractionator d. The liquefied gases containing saturated and unsaturated hydrocarbons of from two to four carbon atoms per molecule collected in the accumulator ii likewise comprise hydrocarbons which may be recycled to increase the ultimate yield of the process. These gases may be forced through a line 555 by means of a pump 55 to the accumulator 8, either directly or by admixture with the liquefied gases passing through line 33, as shown.

In lieu of the absorber E, fractionator t, and associated apparatus, we may recover the valuable hydrocarbons passing through the line lill by conducting them to a fractionating column provided with suitable refrigeration at the top thereof. Byproviding suitable refrigeration at the top of such a fractionator, it is possible to control the top temperature so that gases heavier than methane may be condensed, these gases being returned to the high-pressure accumulator d for reprocessing in the manner described.

In another mode of operation, substantially all of the hydrogen and methane may be removed from the process other than in the manner described. When practicing this method of ,removing hydrogen and methane, the overhead fraction from the fractionator 3, after passing through 'the condenser 26, may be passed thrqugh an indirect heat exchanger of the refrigeration type. In thus passing through this type of heat exchanger, the overhead fraction will be cooled to a temperature sumciently low to retain normally gaseous hydrocarbons of higher molecular Weight than methane in liquid condition. The cooled products may then be passed to a fractionator, maintained under substantially the same pressure as the fractionator 3, with hydrogen and methane being withdrawn from the top. The liquid hydrocarbon collecting in the bottom of such a fractionator is withdrawn therefrom and passed to the heating zone through the line I3 as previously described.

The refrigeration necessary to cool the products to a temperature sufdciently low to maintain gaseous hydrocarbons heavier than methane in liquid condition may be obtained by expanding the dry gas containing hydrogen and methane separated in the process, as for instance through an ejector or expansion valve, and utilizing the cold due to the expansion of the dry gas to cool the overhead fraction passing in indirect heat exchange therewith. f

Each of the fractionators 3, l, 6 and 1 is preferably refluxed with a refluxing medium to accomplish the desired fractionation therein. As a convenient and efficient manner of accomplishing the desired fractionation, a part of the liquid collected in each of the accumulators 8, 9, Il and I2 may be returned to its respective fractionator. This return may be accomplished through a line 56, connected to each accumulator and its associated fractionator by a pump 51. Each of the fractionators may lalso be provided with suitable reboilers. well understood in the art.

It will be understood that while our invention has been described with reference to preferred operating examples, it is not limited in its broader aspects to such operating details as have been set forth hereinabove by way of example, but may .elevated pressure, effecting separation of the conversion products in said separating zone into a gaseous fraction predominating in normally gaseous hydrocarbons and a liquid fraction predominating in normally liquid hydrocarbons, passing the said gaseous fraction to a fractienating zone maintained at a pressure of the same order of magnitude as that of' the separating zone, fractionating the hydrocarbons introduced into said fractionating zone to separate therefrom a 'liquid fraction containing substantially all the normally liquid hydrocarbons introduced into 'said fractionating zone, separately cooling the remaining uncondensed gases from said fractionating zone to condense therefrom a liqueed fraction suitable as feed to the said thermal gas conversion treatment, passing the liquid fraction separated in the said separating zone and the liquid fraction separated in said fractionating zone to a second fractionating zone maintained at a pressure substantially lower than that of the said separating zone, fractionating the hydrocarbons introduced into said second fractionating zone into a normally liquid fraction containing the motor fuel product of the process and a normally gaseous fraction, and returning to said thermal gas conversion treatment the liquefied fraction condensed from the gases from the inst-mentioned fractionating zone and the normally gaseous fraction separated in the said second fractionating zone.

WRIGHT W. GARY.

JAMES S. CAREY. 

